Business machines are often powered by alternating current (AC) supplied via standard power lines. With some machines the required power line AC input varies widely over time. For example, electrophotographic marking machines usually include fusers that produce permanent images by using heat and pressure to fuse toner with substrates, such paper. Such fusers generally use temperature-controlled, AC powered fuser heaters that require large amounts of electrical power when initially heating a pressure roller to a using temperature, less power when actually fusing, and even less power when in stand-by. The fuser heater temperature depends on, among other factors, the electrical power applied to the fuser heater. Other alternating current (AC) business machines also have widely varying electrical power requirements. For example, high volume ink jet printers frequently include AC powered heaters that remove moisture from inked paper to prevent ink smearing. Again, the AC electrical power applied to a heater is usually controlled such that the proper drying temperature is achieved. It should be noted that the AC heaters discussed above are frequently high-power devices that require substantial currents.
Heater temperature regulation is usually performed by a heater controller that limits the electrical power to the heater such that the heater does not overheat (which wastes energy, reduces operating lifetimes, and presents a fire and burn hazard). Prior art heater controllers include simple ON/FF switching devices, cycle stealing, and AC phase control devices. While generally successful, such prior art heater controllers have problems. ON/OFF power switching and cycle stealing lead to low apparent power factors and voltage fluctuations that can cause loss of data while phase control can produce high harmonic content signals, low apparent power factors, and interference with other devices. Indeed, European standards can be difficult to meet using any prior art heater controller.
Low apparent power factors are a significant problem. Consider a machine designed to draw less than 1380 volt-amps. This power rating can be achieved using a 15-ampere service connection. However, a low apparent power factor can cause the instantaneous line current to greatly exceed 15-ampere, even though the time-averaged current may be well below 15-ampere.
In addition to a high power heater, most AC powered business machines also have other electrical power requirements. For example, electrophotographic marking machines have photoreceptor chargers that require high voltages at low currents and electronic subsystems that require low voltages at high currents. Implementing multiple power requirements can be difficult. For example, voltage fluctuations caused by switching power to and from AC heaters can cause lamps to flicker and potential loss of valuable system information.
In view of the foregoing, a new technique of controlling AC heater loads in business machines having multiple power requirements would be useful.